Solid marking materials, in the form of crayons, have long been used for writing, drawing and marking on various surfaces, such as paper, plastic, metal, glass, ceramic, rubber and the like. Crayon compositions are known in the art. For example, U.S. Pat. No. 4,212,786 to Murakami ("the '786 patent") discloses a crayon composition comprising resins, derivatives of sorbitols, glycols and pigment.
Japanese Patent No. 58134166 discloses a glittering crayon composition comprising waxy material, a surface active agent, pigment, colorant and a glittering material.
These prior art patents do not, however, disclose crayon compositions having water soluble and washability properties.
It is desirable to make temporary markings with solid marking materials, such as crayons, and it is desirable to readily remove crayon markings from various surfaces with water. Washable crayon compositions and other washable solid marking compositions are known in the art. U.S. Pat. No. 5,084,493 to Olson et al. ("the '493 patent") discloses a water soluble crayon composition and process for making the composition. The composition of the '493 patent is limited to one or more water soluble block polymers characterized by an ABCBA structure.
U.S. Pat. No. 4,840,669 to Hughes et al. discloses water soluble coloring compositions containing a polymeric thickener, water soluble micro-crystalline wax, coloring and sparkle components.
U.S. Pat. No. 4,978,390 to Snedeker discloses a washable solid marking composition, and U.S. Pat. No. 3,993,492 to Woolly discloses a water soluble transfer coating material and articles incorporating the same, which article may be a water soluble crayon. The compositions of Snedeker and Woolly, however, contain polyethylene glycol, a compound which has been found to leave a ghost image on some rough or nonporous substrates, such as soft plastics and rubber, after the mark has been removed with water.
Prior art crayon compositions incorporating water solubility properties do not completely satisfy all desired performance properties, such as marking characteristics, durability and the like. Thus, there is a need for an improved water soluble crayon composition that combines water solubility with desired performance properties. In particular, a combination of desired performance properties can be difficult to attain as a result of the components used in prior art compositions. Although water soluble crayons are known in the prior art, they are deficient not only in their physical properties but also in their marking characteristics. For example, as stated in the '786 patent at column 1, lines 54-60, water soluble crayon compositions containing cellulose resin or vinyl resin will have high hardness, but cannot be smoothly applicable to surfaces. Crayon compositions containing acrylic resins, phenolic resins and the like will have low hardness and are smoothly applicable, but fail to give uniform drawing lines. In addition, as stated in the '493 patent at column 3, lines 38-43, certain waxes or resins may be sufficiently durable or hard but may be sticky, whereas crayons containing different waxes or resins may have less stickiness but also less durability or hardness. Furthermore, as stated in the '786 patent at column 1, lines 60-66, crayon compositions containing cellulose, vinyl, acrylic and phenolic resins, when in a liquid state, often have high viscosity. This may present difficulty in shaping the composition mixture with molds.
There is also a need for an improved water soluble crayon composition that does not leave a ghost image on rough or nonporous substrates, such as soft plastics and rubber, after the mark has been removed with water. In addition, there is a need for an improved water soluble crayon composition that achieves a high degree of washability from fabrics, wallpaper, upholstery, carpets, painted surfaces and other surfaces.
The water soluble crayon composition of the present invention satisfies these needs, and is an improvement over the conventional crayon compositions known in the art. The water soluble crayon composition of the present invention provides a combination of desired performance properties, such as excellent washability and water solubility with little or no ghosting problems, non-toxicity, suitable hardness and durability, excellent adhesion and drawability, little or no stickiness after hardening and mold release, a higher softening temperature than a typical wax crayon, and low viscosity in a liquid state at elevated temperatures for ease in shaping with molds.
Methods for preparing water soluble crayon compositions are also known in the art. Crayons are generally prepared by combining one or more natural or synthetic waxes, such as water insoluble paraffin, carnauba wax, hydrocarbon waxes and the like, in a molten state, adding a coloring agent to the molten mixture, and pouring the resulting composition into a specified mold and solidifying the composition by cooling. The '493 patent discloses processes for the production of water soluble crayon compositions, and for the manufacture of crayons which utilize a mixture of one or more water soluble block polymers characterized by an ABCBA structure.
Thus, the present invention overcomes the deficiencies associated with the prior art by providing an improved water soluble crayon composition that leaves little, if any, ghost appearance, residue or color after the crayon is washed off a surface, that is non-toxic, has suitable hardness and durability, excellent adhesion and drawability, little or no stickiness after hardening and mold release, a higher softening temperature than a typical wax crayon, and has low viscosity in a liquid state at elevated temperatures for ease in shaping.